The Portuguese believes the pressure of the occasion got to some of his players, with United's poor first-half display compounded by two penalty appeals being rejected after the break.

Fellaini was disappointed by the loss but knows United cannot allow that feeling to fester, with the Red Devils having to prepare for Thursday's trip to Rotterdam to take on Feyenoord as their Europa League campaign gets under way.

"Everyone is disappointed today, which is normal after losing a derby, but this is the fourth game of the season and every team will lose games," the Belgium midfielder said.